The present invention refers to an improved arrangement for the insertion of the electric coils in the stator of an electric motor with the use of automatic equipment.
The stator in electric motors is commonly known to be made up substantially by two basic structures, ie. the stator stack and the various coils of electric wires that are appropriately inserted in the respective slots provided in said stator stack.
During stator manufacturing, use is made of automated machines along with assembly tools and processes which are specifically developed and designed for the insertion of the various coils of electric wires into the respective slots of the stator stack. Such a xe2x80x98dedicatedxe2x80x99 equipment includes a tool which is generally known in the all as xe2x80x9ccoil insertion toolxe2x80x9d and is formed by:
a moving insertion spider provided with moving wire-guide blades,
a container of stationary wire-guide blades,
an insertion blade stack guide.
These terms are generally known to those skilled in the art; however, considering the the matter being dealt with here is a very specialistic one, in order to promote a better understanding of the following description the basic elements of the above cited tool shall be particularly stressed below by using the same terminology as the one used throughout the following description and the appended claims.
Moving Insertion Spider
This is a tool formed by a central rigid body, usually of metal and a substantially cylindrical shape, the side surface of which is provided with a plurality of recesses that are regularly spaced out from each other; these recesses have an elongated shape, are open on the side surface of said cylindrical body, and are arranged so as to enable their inner surface, which is in the form of a ruled surface, ie. a surface generated by the solely translatory, parallel motion of a straight line, to emerge, ie. come out at the bases of said cylindrical body.
In said recesses there are provided, in an alternate arrangement, a plurality of wire-guide blades, which are constituted by elongated members whose outer surface is again in the form of a ruled surface and whose respective axes are parallel to and equidistant from the axis of said cylindrical body.
Container of Stationary Wire-Guide Blades
This member is totally similar to the above described one, so that its description may be omitted here for reasons of conciseness. Anyway, the physical configuration of these two members, and the dimensions thereof, are such as to make it possible for the moving insertion spider to fit into said container of stationary wire-guide blades by simply introducing said moving spider, from the side of said cylindrical body, into the cylindrical space that is delimited externally by the barrier of the wire-guide blades arranged outside the cylindrical body of said container. This is usually possible owing to the fact that the blades arranged on the container and the blades arranged on the moving spider are provided alternately with respect to each other, so that the blades of the moving spider are able to fit into the recesses in the cylindrical body of the container of stationary wire-guide blades.
Blade Stack Guide
The blade stack guide is a cylindrical member formed by a rigid central body, usually of metal, whose side surface is provided with a plurality of recesses that are spaced out regularly from each other; these recesses have an elongated shape, are open on the side surface of said cylindrical body, and are arranged in such a manner as to enable their inner surface, which is in the form of a ruled surface, to emerge, ie. come out at the bases of said cylindrical body. In practice, this blade stack guide is fully similar to the cylindrical body that has been described in connection with both the moving spider and the stationary blade container.
For a more complete information, it should be further noticed here that the structure of the moving spider is sometimes inserted and firmly locked in the container of stationary blades, so that the latter has outwardly a structure that makes it substantially impossible for the two cylindrical bodies to be distinguished from each other. Such a variant, however, is not relevant to the purposes of the present invention, so that its description may be omitted here for reasons of greater clearness.
The procedure followed to assembly the coils in the stator is described shortly below:
for a start, the moving spider is inserted to the desired depth into the container of stationary blades, whereas it will be appreciated that, in the case that these two members are already joined to each other, this phase is of course omitted; anyway, a corresponding plurality of parallel gaps extending in the lengthwise direction of the blades are created between the stationary blades and the contiguous moving blades;
thereupon, the coils are appropriately inserted, in a basically per se known manner, into said gaps with the related wires that distribute up to a certain height, within and along said gaps;
then the blade stack guide is mounted within the perimeter delimited, on the opposite side with respect to the cylindrical body, by the extreme portions of the same blades; this is obviously allowed for by the fact that the recesses in the blade stack guide are provided so as to be able to accomodate said extreme portions of the blades, so that the guiding function of such blades in the following phase is ensured;
the coil insertion operation can at this point be started, which consists mainly in raising the moving spider and allowing the same to fit into the slots of the stator stack that will have in the meantime been duly prepared and arranged.
It is exactly during this operation that, owing to the effect of the various combined forces and reactions, the blades can be noticed to be stressed into flexing, both outwardly and inwardly, and even into twisting.
Since these blades are provided, on their outwards facing edges, with two sharp corners, that we shall call xe2x80x9cslot lining protection bordersxe2x80x9d here and have the task of fitting in between the inlet edges of the sheath (also called xe2x80x9cslot liningxe2x80x9d) used to protect the slot, it clearly ensues that even these protective borders undergo said flexural and/or torsional stresses, ie. in particular against the wires of the adjacent wire coils.
This occurrence gives usually rise to two kinds of drawbacks: the first one derives from said borders being subject to rapid wear-out owing to the wires of the coils rubbing against them along almost the entire length thereof; it therefore becomes necessary for these tools to be replaced quite frequently and this fact puts heavy penalties in terms of costs considering both the unit cost of these tools and the quite significant number in which they are necessarily used in such an industrial process on a very large scale as it is usually required today for a competitive production.
The second one of said drawbacks is due to the fact that said wires, by rubbing against said sharp corners of said edges, are exposed to being scratched or indented; in particular, it is their outer insulating enamel layer that is in this way most easily damaged, thereby making it easy for the coil to break down and causing adjacent damaged wires to short-circuit.
An arrangement for the insertion of coils in a stator stack wherein the blades are provided with grooves is known, for example, from U.S. Pat. No. 4,588,349 and JP 61 109442. However, the technical solutions described in these documents are only effective to avoid some problems related to the frictional contact between a coil and blades, and to provide an improved coil fitting system able of smoothly fitting coils in the slots in an armature core, but no improvement is offered to prevent the outward and inward bending stresses and torsional stresses of the wire-guide blades.
It would therefore be desirable, and it is actually a main purpose of the present invention, to provide one or more improved arrangements that are not only capable of preventing said wire-guide blades from undergoing both outward and inward bending stresses and torsional stresses as coils are being inserted in the related stator stack, but are also simple, unexpensive, capable of being implemented with readily available techniques and means, and do not require any modification to be introduced in the manufacturing process.